zlaqr1 man page on Scientific
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ZLAQR1(1) LAPACK auxiliary routine (version 3.2) ZLAQR1(1)
NAME
SYNOPSIS
SUBROUTINE ZLAQR1( N, H, LDH, S1, S2, V )
COMPLEX*16 S1, S2
INTEGER LDH, N
COMPLEX*16 H( LDH, * ), V( * )
COMPLEX*16 ZERO
PARAMETER ( ZERO = ( 0.0d0, 0.0d0 ) )
DOUBLE PRECISION RZERO
PARAMETER ( RZERO = 0.0d0 )
COMPLEX*16 CDUM, H21S, H31S
DOUBLE PRECISION S
INTRINSIC ABS, DBLE, DIMAG
DOUBLE PRECISION CABS1
CABS1( CDUM ) = ABS( DBLE( CDUM ) ) + ABS( DIMAG( CDUM ) )
IF( N.EQ.2 ) THEN
S = CABS1( H( 1, 1 )-S2 ) + CABS1( H( 2, 1 ) )
IF( S.EQ.RZERO ) THEN
V( 1 ) = ZERO
V( 2 ) = ZERO
ELSE
H21S = H( 2, 1 ) / S
V( 1 ) = H21S*H( 1, 2 ) + ( H( 1, 1 )-S1 )* ( ( H( 1, 1
)-S2 ) / S )
V( 2 ) = H21S*( H( 1, 1 )+H( 2, 2 )-S1-S2 )
END IF
ELSE
S = CABS1( H( 1, 1 )-S2 ) + CABS1( H( 2, 1 ) ) +
CABS1( H( 3, 1 ) )
IF( S.EQ.ZERO ) THEN
V( 1 ) = ZERO
V( 2 ) = ZERO
V( 3 ) = ZERO
ELSE
H21S = H( 2, 1 ) / S
H31S = H( 3, 1 ) / S
V( 1 ) = ( H( 1, 1 )-S1 )*( ( H( 1, 1 )-S2 ) / S ) + H(
1, 2 )*H21S + H( 1, 3 )*H31S
V( 2 ) = H21S*( H( 1, 1 )+H( 2, 2 )-S1-S2 ) + H( 2, 3
)*H31S
V( 3 ) = H31S*( H( 1, 1 )+H( 3, 3 )-S1-S2 ) + H21S*H(
3, 2 )
END IF
END IF
END
PURPOSE
LAPACK auxiliary routine (versioNovember 2008 ZLAQR1(1)
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